1. Technical Field
The present invention relates to a discharge lamp driving device, a light source device, a projector, and a discharge lamp driving method.
2. Related Art
In recent years, energy saving for projectors has been demanded. Therefore, there has been proposed a projector implemented with various lighting modes such as a low power mode for reducing driving power to a lamp to be lower than usual, a dimming mode for changing the driving power in synchronization with an image signal, and a standby mode for reducing the driving power when a video signal is not input from the outside. For example, in the low power mode, since the driving power supplied to the lamp is low, a load on electrodes decreases and the life of the lamp is increased.
However, when the driving power is smaller than rated power, protrusions at electrode distal ends cannot be sufficiently melted. When lighting is continued for a long time, the protrusions are worn and reduced. The reduction of the protrusions leads to an increase in an inter-electrode distance and causes deterioration in illuminance. That is, when the shape of the protrusions at the electrode distal ends cannot be maintained, the advantage of the low power mode cannot be utilized and the life of the lamp decreases. Therefore, in order to solve this problem, for example, as disclosed in JP-A-2008-270058 (Patent Literature 1), there has been proposed a discharge lamp lighting device and a projector that drive a lamp in a refresh lighting mode for facilitating melting of protrusions of electrodes in a predetermined period after lamp lighting.
In a lighting mode with relatively low driving power, since heat load applied to electrodes is small, protrusions at electrode distal ends are thinned. Therefore, when, under conditions same as conditions for a lamp on which a mode with relatively high driving power is executed, the refresh lighting mode is executed on a lamp (a discharge lamp) on which the lighting mode with the relatively low driving power is executed, the heat load is excessively applied to the thinned protrusions. Consequently, the protrusions disappear and flickering of the discharge lamp sometimes occurs.